This invention relates to a new family of luminescent materials or phosphors that are photoluminescent, cathodoluminescent and, in some cases, roentgenoluminescent.
Luminescent mixed sulfides of different host cations are known in the art. U.S. Pat. No. 3,174,939 to L. Suchow, for example, discloses mixed sulfides of divalent cadmium and trivalent indium activated with Dy, Ho, Er, Tm, Yb and Lu. These prior phosphors are disclosed to have a spinel crystal structure and to emit infrared radiation when excited with ultraviolet light from a xenon lamp.
The novel luminescent materials or phosphors are mixed sulfides of monovalent and trivalent host cations. The monovalent host cations are at least one of the alkali metals including sodium, potassium, rubidium, and cesium. The trivalent host cations are at least one of gadolinium, lanthanum, lutetium, scandium and yttrium. The phosphors contain 0.00005 to 0.05 mole per mole of phosphor of activating cations, which may be one or more of trivalent arsenic, bismuth, cerium, dysprosium, erbium, praseodymium, antimony, samarium, terbium and thulium; divalent europium, manganese, lead, and tin; and monovalent silver, copper and thallium. The novel phosphors have a rhombohedral crystal structure similar to that of alpha sodium ferric oxide and the empirical or molecular formula EQU (.alpha. Ma .gamma. Mc .delta./2 Md) (.beta. Mb .delta./2 Md .epsilon. Me)S.sub.2
where:
Ma is at least one of monovalent Na, K, Rb and Cs, PA1 Mb is at least one of trivalent Gd, La, Lu, Sc and Y, PA1 Mc is at least one of the above-mentioned activating monovalent cations, PA1 Md is at least one of the above-mentioned activating divalent cations, PA1 Me is at least one of the above-mentioned activating trivalent cations, PA1 S is sulfur, PA1 .alpha. is 1.00 minus .gamma. minus .delta./2 mol, PA1 .beta. is 1.00 minus .epsilon. minus .delta./2 mol, PA1 .gamma., .delta. and .epsilon. are each in the range of 0.0 to 0.05 mol, and PA1 .gamma. plus .delta. plus .epsilon. is in the range of 0.00005 to 0.05 mol.
The preferred groups of the novel phosphors are KYS.sub.2 and NaYS.sub.2 host crystals, each activated with one of Ag.sup.1.sup.+, Cu.sup.1.sup.+, Eu.sup.2.sup.+, Ce.sup.3.sup.+, and Bi.sup.3.sup.+.